The term organic contaminants in papermaking process refers to the interfering substances that have permanent or temporary physical tackiness and may influence runnability of paper machines and harm the quality of the paper or board product. The organic contaminants can be divided into two types depending on their sources, that is, pitch and stickies. Pitch refers to hydrophobic colloidal particles, including those released from woods, such as resin acids, fatty acids, triglycerides and unsaponifiable like sterol esters and waxes, and those introduced into the pulping process such as defoamers, rosin size, coatings, some components of alkaline sizing agents, etc. The stickies refer to adhesive materials derived from recycled fibers. The mixtures generally comprise pressure-sensitive adhesives, hot-melt adhesives, latex binders from coatings, ink adhesives, wet-strength resins, paraffin waxes, and other polymers.
When conditions of the paper machine system (for example, pH, temperature, water hardness, or shearing force of the system) suddenly change, the two types of tacky organic contaminants are apt to aggregate and deposit in the fabrics, felts, rolls, machine wires, belts, presses, and dryer surfaces of the paper machine system. As a result, the frequency of wash-ups, boil-outs, and paper breaks on the machine increase. Moreover, when formed deposits appear on final products in the form of paper defects such as pinholes, spots, specks, and others, paper quality will definitely be degraded and operational problems relating to the subsequent coating or printing processes will also occur.
Currently, with the rising use of recycled paper and high-yield mechanical pulp as raw materials, the increasing reuse of paper machine white water, and the increasing content of contaminants in recycled fiber, problems caused by pitch and stickies are increasing.
In the pulping and papermaking industry, chemical processing methods are generally used to inhibit or control the deposition of organic contaminants, thus solving the aforementioned problems. There are three chemical treatments that are commonly applied in paper mills: detackification, dispersion, and fixation.
The chemical compositions of organic contaminants produced in the process of pulping and papermaking may not be that similar, but, they have the common physical properties of low melting temperature/glass transition temperature and low surface energy (high hydrophobicity). This means that they are apt to agglomerate into larger particles when in water and adhere to interfaces of metal, plastics and other synthetic materials in the papermaking system to form deposits.
Inorganic passivators, including talc, bentonite, alum and others, were previously used widely as detackifiers in pulping and papermaking processes. Despite the advantage of low cost, they are usually used in a large amount, and the huge variance of their dispersity in water has limited their detackifying effectiveness in practice.
Now, detackifiers that are commonly used include mainly polymers of high hydrophilicity, for example, synthetic products of polyvinyl alcohol-vinyl acetate (U.S. Pat. Nos. 4,871,424 and 4,886,575), polyethylene glycol and modified polyethylene glycol (U.S. Patent Application No. 2008/0029231), polyethylene oxide and modified polyethylene oxide (European patent application No. 1993/0568229), polyacrylate-styrene (U.S. Patent Application Nos. 2002/0148576 and 2003/0150578), etc. Detackifiers commonly used also include natural products such as non-ionic cellulose ether (U.S. Pat. Nos. 4,698,133 and 5,074,961), serum albumin and globulin (U.S. Pat. No. 5,885,419).
For the detackifiers disclosed in the aforementioned references to play the function of effectively inhibiting organic deposits, they must be efficiently and selectively adsorbed to the hydrophobic surface of particles in a physical or chemical manner, and then these particles can be stably dispersed in water systems due to their increased surface energy. However, sources of pulp materials and application of chemical additives in paper mills vary enormously. This means that deposits like pitch and stickies have particular and complex categories and different consistencies as well. Therefore, detackifiers containing a single component cannot effectively solve the issues of deposition of organic contaminants.
U.S. Pat. No. 5,540,814 discloses a method of using modified cationic kaolin to remove stickies in wastepaper. This method can effectively reduce the number of stickies and dirt in finished pulp or paper products through sufficient surface cationization of an anionic kaolin with epichlorohydrin dimethylamine polymer or poly diallyl dimethyl ammonium halide. In addition, it can also facilitate the removal of ink by centrifugal cleaners.
U.S. Pat. No. 6,977,027 discloses a process to control stickies formation and remove anionic trashes from recycled old corrugated container furnish, old newsprint furnish, deinking pulp furnish, old magazine grade furnish, etc. by adding talc and tertiary or quaternary amine through the means of blending. Through this method, the forming of stickies can be effectively inhibited, and the amount of anionic trashes in the recycled fibers can be reduced.
U.S. Pat. Nos. 5,292,403 and 5,556,510 disclose a method of using a composite detackifier comprising a charged polymer and an oppositely charged surfactant to inhibit the deposition of organic contaminants in a pulping and papermaking system. The former (U.S. Pat. No. 5,292,403) applies carboxymethyl cellulose, carboxymethylated starch or polyacrylic acid, etc. as the anionic polymer, and for example, aliphatic amine or alkyl imidazoline, etc. as the cationic surfactant; while the latter (U.S. Pat. No. 5,556,510) applies cationic starch as cationic polymer and, for example, sodium soap of tall oil fatty acid as the anionic surfactant. Both of these detackifiers are highly surface active which may reduce the tackiness of pitch and stickies, thus preventing the deposition of such contaminants on deposition prone surfaces of the paper machine.
U.S. Pat. No. 5,723,021 discloses a method for inhibiting deposition of contaminants in a pulping and papermaking system. Specifically, the composite detackifier hereinto consists of three components: a polyvinyl alcohol having 50-100% hydrolysis, a high molecular weight gelatin protein, and a cationic polymer represented by polyamine or polyethyleneimine. As revealed from the results of examples, the above said tri-component detackifier has such advantages as high efficiency, good adaptability and good performance over a broad range of pH and water hardness. Additionally, there is no obvious negative impact on wet end retention and sizing.
U.S. Pat. No. 6,051,160 discloses a composition of detackifier consisting of a derivatized cationic guar and a styrene-maleic anhydride copolymer. This composition can be used as a pitch control agent in the process of pulping and papermaking, and it can also be used for the ionic balance of the papermaking system to some extent.
U.S. Pat. No. 6,461,477 discloses a method for inhibiting the deposition of organic contaminants in pulping and papermaking system. Specifically, this method is to add a structured protein (e.g., whey protein) and at least one of cationic polymer (e.g., poly (diallyldimethylammonium chloride), cationic starch, cationic cellulose derivatives, alum, etc.) into the pulp, or apply them to the deposition prone surfaces of papermaking machinery and equipment, so as to minimize the deposition of pitch and stickies.
U.S. patent application No. 2008/0169073 discloses a method for inhibiting the deposition of organic contaminants in pulping and papermaking system. Specifically, In this method, a combination of a lipase and a non-ionic polymeric detackifier (e.g., hydrophobically modified hydroxyethyl methyl cellulose, and/or polyvinyl acetate having 50-100% hydrolysis) are added into the pulp, or applied to the deposition prone process equipment surfaces, so as to minimize the deposition of pitch and stickies in papermaking mills who use virgin pulp, recycled pulp or the combinations.
U.S. Pat. No. 7,166,192 discloses a method of adding the combination of hydrophobically modified hydroxyethyl methyl cellulose and cationic polymers to control pitch and stickies. It can be seen from the results of turbidity and UV-Vis absorption spectra disclosed from the examples that, this method is mainly to help improving the role of the cationic polymer in retaining pitch and stickies on the paper fibers, by using hydrophobically modified hydroxyethyl cellulose ether, so as to realize the purpose of reducing the total deposits and optimizing the amount of papermaking retention aids. Obviously, this method is neither to disperse the pitch and stickies in the water system, nor to detackify them, but to fix them onto paper fibers, and then remove them from the paper machine system by retaining them in the finished paper.
To conclude, the aforementioned prior art disclosed methods for detackifying or re-dispersing or fixing the organic contaminants onto the paper fibers, in the process of pulping and papermaking through adding some substance or composition, so as to control or inhibit the deposition of the organic contaminants, namely, the pitch and stickies.